To date, automotive tail lights and similar products have been produced using complicated and/or costly manufacturing procedures. This high degree of complexity has been necessitated by the complexity of such parts, which have typically incorporated several different components within a frame. For example, a standard tail light usually includes clear lenses, colored lenses, reflective parts, etc. These separate pieces were arranged in the appropriate order and bound together within a frame which was then attached to the automobile.
Another approach has been to mold a first part of the lens in one tool and to then transfer this first molded part to a second injection molding machine having a second tool. The first molded part is inserted into the second machine and a new color may be injected onto the first part to create a two color lens. The process may be repeated as many times as necessary to produce the desired tail light assembly. Obviously, this approach is costly since it requires at least two injection molding machines and at least two tools.
Alternatively, multi-shot injection molding machines have been used. Multi-shot is a process using more than one injection barrel to obtain a multi-colored part. This process is very expensive, as it requires specially designed injection barrels and tools. In a typical application, a clear coating might be initially injected onto the three-dimensional piece, and then various colored or reflective segments would be injected, using different injection barrels, onto the base piece in the appropriate order. While an advance over the framing of individual pieces, there are a number of shortcomings associated with multi-shot injection, including the previously discussed increased tooling costs, longer processing cycle times, additional part scrap and the need to maintain additional material inventory.
More recently, an in-mold processing variation of the framing technique has been proposed in U.S. Pat. No. 5,275,764. The '764 patent suggests that one or more colored or reflective elements be placed into a single mold cavity. Molten plastic is then injected into the mold cavity such that the individual colored or reflective elements are combined in a one-piece assembly having one or more colors or reflective means in a single lens panel. It is claimed that since the elements may be of uniform thickness and density, this one-piece assembly provides more even color distribution when lit. In addition, this one-piece assembly is said to reduce cost and manufacturing time in comparison to the tail lights of the prior art.